A process and an apparatus of the aforementioned kind have become known from U.S. Pat. No. 4,539,231 A.
In this prior art process an optical lens made of a plastic material is worked by grinding. According to a first described embodiment a liquid cooling agent is continuously sprayed onto the lens blank during grinding in order to avoid that the lens is inadmissibly heated up and deformed during the grinding process.
According to another described embodiment the lens is worked under dry conditions, wherein the grinding tool is configured such that only individual small grinding particles are generated. The particles are blown off and exhausted by means of an air stream. In this connection the plastic material is specified to be CR-39 or a polycarbonate.
Besides this prior art grinding process in which grain-like grinding chips, i.e. individual small particles, are cut off, there exists still another known chip-cutting working process for plastic material optical lenses, namely the so-called “diamond-lathing” process.
In this prior art process a relatively elongate chip is generated, as is typical for all lathing or turning processes. These so-called “curled chips” present problems with respect to disposing same because they tend to become entangled with one another so that they may not be disposed easily by means of an air stream or the like.
One has, therefore, already attempted to prevent the generation of such curled chips by modifying the cutting program, i.e. the machine control for the lathe, such that e.g. after each revolution of the lens blank the lathing tool or cutter was moved back to the position at which it had started the just terminated revolution for a short period of time. As a consequence, the cutting edge was moved to a position that had already been worked and, therefore, was void of material for a short period of time such that the generated chip was interrupted at that moment.
This approach, however, has the disadvantage that lathing chips are still generated, the length of which corresponding to an entire periphery of the respective revolution. Although these chips are somewhat shorter as compared to those of the type mentioned before, an entanglement of these chips may, however likewise not be excluded.
Moreover, this approach has the disadvantage that the periodical interruption of the lathing process results in an overall extension in time of the working process.
Further, the periodical switching of the lathing tool results in oscillations within the lathe, and, finally, the resulting surface quality is also negatively affected.
It is, therefore, an object underlying the invention to improve a process and an apparatus of the type specified at the outset such that the aforementioned disadvantages are avoided.
In particular, the inherent advantages of the diamond-lathing process shall be retained, whereas, on the other hand, the above-mentioned disadvantages shall be avoided, in particular the generation of elongate lathing chips.